Equipment for dispensing a cryogenic liquefied gas onto a surface or object to be sharply cooled has been proposed heretofore. These are designed to utilize liquefied gas such as helium, nitrogen, oxygen, air, carbon dioxide, etc., stored in a suitable container. The liquid coolant is supplied therefrom to a dispensing port or nozzle in various ways including applying heat electrically or otherwise to the coolant to vaporize the liquid. Other designers pressurize the storage container to produce coolant flow by introducing air under pressure into the storage container while other designers provide the storage container with a normally open vent which is closed to initiate coolant flow whereby the vapor pressure which develops within the container produces a flow of coolant to the dispensing nozzle. The pressure build-up is slow and uncertain and varies widely depending on the volume of the vapor space and the quantity of liquid coolant in the storage chamber, the rate of heat leakage into the container and other factors.
One category of prior cryogenic devices dispenses a jet of coolant vapor directly onto the area to be cooled whereas those of another category confine the stream of coolant vapor to a flow passage typically provided with a return bend sector formed of excellent heat conductive material and venting to the atmosphere at a remote point. The heat conducting member can be placed close to or in contact with the surface to be cooled without risking direct contact of the gas coolant with that surface.
It has been recognized that it would be advantageous to deliver coolant in liquid phase onto or in close proximity to the area to be sharply cooled in order to utilize the latent heat or vaporization of the coolant as it changes to the gas phase. However, this presents numerous serious problems which have not been resolved prior to this invention. Foremost among these problems is control of the liquid coolant delivered and the amount of cooling provided. It is manifestly not feasible to deliver even a minute stream of liquid coolant onto living tissue. Not only is the cooling capacity of liquid coolant very great but, upon entering the atmosphere, becomes rapidly superheated with resultant vigorous boiling and uncontrolled dispersal.
Attempts have been made to create a spray of liquefied coolant particles of which can be dispensed directly onto the area to be necrotized. However, the equipment heretofore provided for this purpose is subject to many shortcomings and disadvantages including instability and erratic coolant flow, inability to form a stable, small diameter jet, fluctuating spurts of the coolant jet, time delay and waste involved in establishing a coolant jet, continuing change in the rate of flow, the highly inefficient use of a given charge of liquid coolant, and the need for recharging a hand-held reservoir several times a day.